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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg

[1.34] Sunspot Gyroresonance Emission at 17 GHz: A Statistical Study

A. Vourlidas, D. E. Gary (Caltech), K. Shibasaki (Nobeyama Radio Observatory)

Our statistical study is based on a compilation of the daily Nobeyama Radioheliograph full-disk maps obtained at 17 GHz between July 1992 -- December 1994. It includes 533 active regions, 20% of which appear to have gyroresonance cores during some part of their disk crossing. At least one of the regions reaches coronal temperatures (T>10^6 K) while several others show a polarization reversal at the extreme limb. Our study indicates that the gyroresonance cores are polarized in the sense of the x-mode and are due to s=3 (B=2024 G) and/or s=4 (B=1518 G) gyroresonance absorption in the transition region and/or corona. We also investigate the dependence between various physical quantities such as brightness temperature, degree of polarization, spot area, photospheric magnetic field and heliographic longitude and comment on the polarization reversals at the limb. A more detailed study of individual active regions, that have been also observed with the Owens Valley Solar Array, will follow.

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